Moreover, the same matter occurs in a report with 49220 lines fetched from Database.

Could it be linked to the fact that these reports use a pivot table to perform a second aggregation phase?

The final Pivot view is about 10 columns by 10 lines.
Cause
The Number of Rows setting was verified within OBIEE 11.1.1.5.

Capacity Management > Performance

Maximum Number of Rows Processed when Rendering a Table View

This setting limits how much data is retrieved from the BI Server and processed. The default value is 65000.

Reducing the maximum number of rows processed can significantly improve performance by reducing the system resources that can be consumed by a given user session.

Number of Rows 65000

It was found that the cause was the Pivot Table (which generally have more performance overheads when compared to a standard Table).
Solution
Within the instanceconfig.xml file in 10g you would have had to adjust the limits in your file for the parameters below.

In OBIEE 11g, these values below are discussed in the following Guides.

If changes are made to the instanceconfig.xml file please carefully refer to the section stated below:
(Section 3.4, “Using a Text Editor to Update Configuration Settings.”)

When the following changes were made to the instanceconfig.xml file, this fixed the issue.

10000005000000

Oracle suggests that “These values were specific to this environment and the reports being run by that organisation. Other readers should note that increasing these values to too high a level may have an impact on performance (which is hardware dependent).”